The now-retracted paper claimed that Crispr caused nearly 2,000 unexpected mutations—ten times previously observed off-target rates—in two mice that it cured of blindness. But just as that evidence should never have been enough to squash Crispr’s clinical potential, neither does retracting said paper prove it. If anything, the kerfuffle just proves how young the field is. There’s so little published data about the potential for Crispr’s unintended cuts that this single, flawed paper had an outsized effect on perception of the field. Can Crispr be safely used in humans? Retraction or not, it’s still an open question.

Not that scientists haven’t been trying to answer it. But developing trustworthy methods to detect off-target mutations has proven challenging. So far, they’ve come with about a half-dozen approaches; the fastest and most economical is something called targeted sequencing, where researchers look for rogue snips in areas an algorithm suspects they might show up. But that method won’t detect mutations that pop up in utterly unexpected places.